{{Article summary text|This article will provide an example of how to install and configure Arch Linux with Logical Volume Manager (LVM).}}

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{{Related|dm-crypt/Encrypting an entire system#LVM on LUKS}}

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{{Article summary heading|Required software}}

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{{Related|dm-crypt/Encrypting an entire system#LUKS on LVM}}

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{{Article summary text|{{pkg|lvm2}}}}

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{{Related|Resizing LVM-on-LUKS}}

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{{Article summary heading|Related}}

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{{Related|Create root filesystem snapshots with LVM}}

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{{Article summary wiki|Software RAID and LVM}}

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{{Related articles end}}

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{{Article summary wiki|System Encryption with LUKS}}

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From [[Wikipedia:Logical Volume Manager (Linux)]]:

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{{Article summary wiki|Encrypted LVM}}

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:LVM is a [[Wikipedia:logical volume management|logical volume manager]] for the [[Wikipedia:Linux kernel|Linux kernel]]; it manages disk drives and similar mass-storage devices.

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{{Article summary end}}

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== Introduction ==

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== LVM Building Blocks ==

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{{Wikipedia|Logical Volume Manager (Linux)}}

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Logical Volume Management utilizes the kernel's [http://sources.redhat.com/dm/ device-mapper] feature to provide a system of partitions independent of underlying disk layout. With LVM you abstract your storage and have "virtual partitions", making [[#Resizing volumes|extending/shrinking]] easier (subject to potential filesystem limitations).

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=== LVM Building Blocks ===

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Virtual partitions allow addition and removal without worry of whether you have enough contiguous space on a particular disk, getting caught up fdisking a disk in use (and wondering whether the kernel is using the old or new partition table), or, having to move other partitions out of the way. This is strictly an ease-of-management solution: LVM adds no security.

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Logical Volume Management makes use of the [http://sources.redhat.com/dm/ device-mapper] feature of the Linux kernel to provide a system of partitions that is independent of the underlying disk's layout. With LVM you can abstract your storage space and have "virtual partitions" which makes it easier to extend and shrink partitions (subject to the filesystem you use allowing this) and add/remove partitions without worrying about whether you have enough contiguous space on a particular disk, without getting caught up in the problems of fdisking a disk that is in use (and wondering whether the kernel is using the old or new partition table) and without having to move other partition out of the way. This is strictly an ease-of-management issue: it does not provide any additional security. However, it sits nicely with the other two technologies we are using.

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Basic building blocks of LVM:

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The basic building blocks of LVM are:

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; Physical volume (PV): Partition on hard disk (or even the disk itself or loopback file) on which you can have volume groups. It has a special header and is divided into physical extents. Think of physical volumes as big building blocks used to build your hard drive.

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; Volume group (VG): Group of physical volumes used as a storage volume (as one disk). They contain logical volumes. Think of volume groups as hard drives.

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* '''Physical volume (PV)''': Partition on hard disk (or even hard disk itself or loopback file) on which you can have volume groups. It has a special header and is divided into physical extents. Think of physical volumes as big building blocks which can be used to build your hard drive.

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; Logical volume (LV): A "virtual/logical partition" that resides in a volume group and is composed of physical extents. Think of logical volumes as normal partitions.

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* '''Volume group (VG)''': Group of physical volumes that are used as storage volume (as one disk). They contain logical volumes. Think of volume groups as hard drives.

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; Physical extent (PE): The smallest size in the physical volume that can be assigned to a logical volume (default 4 MiB). Think of physical extents as parts of disks that can be allocated to any partition.

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* '''Logical volume (LV)''': A "virtual/logical partition" that resides in a volume group and is composed of physical extents. Think of logical volumes as normal partitions.

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* '''Physical extent (PE)''': A small part of a disk (usually 4MB) that can be assigned to a logical Volume. Think of physical extents as parts of disks that can be allocated to any partition.

LVM gives you more flexibility than just using normal hard drive partitions:

LVM gives you more flexibility than just using normal hard drive partitions:

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* Use any number of disks as one big disk.

* Use any number of disks as one big disk.

* Have logical volumes stretched over several disks.

* Have logical volumes stretched over several disks.

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* Create small logical volumes and resize them "dynamically" as they get more filled.

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* Create small logical volumes and resize them "dynamically" as they get filled up.

* Resize logical volumes regardless of their order on disk. It does not depend on the position of the LV within VG, there is no need to ensure surrounding available space.

* Resize logical volumes regardless of their order on disk. It does not depend on the position of the LV within VG, there is no need to ensure surrounding available space.

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* Resize/create/delete logical and physical volumes online. Filesystems on them still need to be resized, but some support online resizing.

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* Resize/create/delete logical and physical volumes online. File systems on them still need to be resized, but some (such as ext4) support online resizing.

* Online/live migration of LV being used by services to different disks without having to restart services.

* Online/live migration of LV being used by services to different disks without having to restart services.

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* Snapshots allow you to backup a frozen copy of the filesystem, while keeping service downtime to a minimum.

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* Snapshots allow you to backup a frozen copy of the file system, while keeping service downtime to a minimum.

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* Support for various device-mapper targets, including transparent filesystem encryption and caching of frequently used data. This allows creating a system with (one or more) physical disks (encrypted with LUKS) and [[dm-crypt/Encrypting an entire system#LVM on LUKS|LVM on top]] to allow for easy resizing and management of separate volumes (e.g. for {{ic|/}}, {{ic|/home}}, {{ic|/backup}}, etc.) without the hassle of entering a key multiple times on boot.

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These can be very helpful in a server situation, desktop less so, but you must decide if the features are worth the abstraction.

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=== Disadvantages ===

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== Disadvantages ==

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* Linux exclusive (almost). There is no official support in most other OS (FreeBSD, Windows..).

* Additional steps in setting up the system, more complicated.

* Additional steps in setting up the system, more complicated.

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* If you use the [[btrfs]] filesystem, its Subvolume feature will also give you the benefit of having a flexible layout. In that case, using the additional Abstraction layer of LVM may be unnecessary.

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* If dual-booting, note that Windows does not support LVM; you will be unable to access any LVM partitions from Windows.

== Installing Arch Linux on LVM ==

== Installing Arch Linux on LVM ==

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You should create your LVM Volumes between the [[Partitioning]] and [[File_Systems#Step_2:_create_the_new_file_system|mkfs]] steps of the Installation Procedure. Instead of directly formating a partition to be you root file file-system, it will be created inside a logical volume (LV).

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You should create your LVM Volumes between the [[partitioning]] and [[File systems#Create a file system|formatting]] steps of the [[Installation guide|installation procedure]]. Instead of directly formatting a partition to be your root file system, the file system will be created inside a logical volume (LV).

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Make sure the {{pkg|lvm2}} package is [[installed]].

Quick overview:

Quick overview:

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* Create partition(s) where your PV will reside. Set the partition type to 'Linux LVM', which is 8e if you use MBR, 8e00 for GPT.

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* Create your physical volumes (PV). If you have one disk it is best to just create one PV in one large partition. If you have multiple disks you can create partitions on each of them and create a PV on each partition.

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* Create your volume group (VG) and add all the PV to it.

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* Create logical volumes (LV) inside your VG.

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* Continue with “Format the partitions” step of Beginners Guide.

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* When you reach the “Create initial ramdisk environment” step in the Beginners Guide, add the lvm hook to mkinitcpio.conf (see below for details).

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{{Warning|{{ic|/boot}} cannot reside in LVM when using [[GRUB Legacy]], which does not support LVM. [[GRUB]] users do not have this limitation. If you need to use GRUB Legacy, you must create a separate /boot partition and format it directly. }}

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* Create [[Partitioning|partition(s)]] where your PV(s) will reside.

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** If you use Master Boot Record partition table, set the [[Wikipedia:Partition type|partition type ID]] to {{ic|8e}} (partition type {{ic|Linux LVM}} in ''fdisk'').

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** If you use GUID Partition Table, set the [[Wikipedia:GUID Partition Table#Partition type GUIDs|partition type GUID]] to {{ic|E6D6D379-F507-44C2-A23C-238F2A3DF928}} (partition type {{ic|Linux LVM}} in ''fdisk'' and {{ic|8e00}} in ''gdisk'').

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* Create your physical volumes (PVs). If you have one disk it is best to just create one PV in one large partition. If you have multiple disks you can create partitions on each of them and create a PV on each partition.

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* Create your volume group (VG) and add all PVs to it.

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* Create logical volumes (LVs) inside that VG.

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* Continue with [[Installation guide#Format the partitions]].

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* When you reach the “Create initial ramdisk environment” step in the Installation guide, add the {{ic|lvm}} hook to {{ic|/etc/mkinitcpio.conf}} (see below for details).

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{{Warning|{{ic|/boot}} cannot reside in LVM when using a boot loader which does not support LVM; you must create a separate {{ic|/boot}} partition and format it directly. Only [[GRUB]] is known to support LVM.}}

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=== Create partitions ===

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If LVM has to be set on the entire disk, there is no need to create any partitions.

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Otherwise, [[partition]] the device as required before configuring LVM.

=== Create physical volumes ===

=== Create physical volumes ===

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Make sure you target the right partitions! To find the partitions with type 'Linux LVM':

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To list all your devices capable of being used as a physical volume:

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* MBR system: {{Ic|fdisk -l}}

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* GPT system: {{Ic|lsblk}} and then {{Ic|gdisk -l ''disk-device''}}

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# lvmdiskscan

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{{Warning|Make sure you target the correct device, or below commands will result in data loss!}}

Create a physical volume on them:

Create a physical volume on them:

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# pvcreate ''disk-device''

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''disk-device'' may be e.g. /dev/sda2.

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# pvcreate ''DEVICE''

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This command creates a header on each partition so it can be used for LVM.

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This command creates a header on each device so it can be used for LVM. As defined in [[#LVM Building Blocks]], ''DEVICE'' can be a disk (e.g. {{ic|/dev/sda}}), a partition (e.g. {{ic|/dev/sda2}}) or a loop back device. For example:

Next step is to create a volume group on this physical volume. First you need to create a volume group on one of the new partitions and then add to it all other physical volumes you want to have in it:

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The next step is to create a volume group on this physical volume.

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First you need to create a volume group on one of the physical volumes:

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# vgcreate <''volume_group''> <''physical_volume''>

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See {{man|8|lvm}} for a list of valid characters for volume group names.

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For example:

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# vgcreate VolGroup00 /dev/sda2

# vgcreate VolGroup00 /dev/sda2

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Then add to it all other physical volumes you want to have in it:

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# vgextend <''volume_group''> <''physical_volume''>

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# vgextend <''volume_group''> <''another_physical_volume''>

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# ...

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For example:

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# vgextend VolGroup00 /dev/sdb1

# vgextend VolGroup00 /dev/sdb1

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Also you can use any other name you like instead of VolGroup00 for a volume group when creating it. You can track how your volume group grows with:

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# vgextend VolGroup00 /dev/sdc

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You can track how your volume group grows with:

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# vgdisplay

# vgdisplay

{{Note|You can create more than one volume group if you need to, but then you will not have all your storage presented as one disk.}}

{{Note|You can create more than one volume group if you need to, but then you will not have all your storage presented as one disk.}}

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=== Create in one step ===

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LVM allows you to combine the creation of a volume group and the physical volumes in one easy step. For example, to create the group VolGroup00 with the three devices mentioned above, you can run:

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# vgcreate VolGroup00 /dev/sda2 /dev/sdb1 /dev/sdc

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This command will first set up the three partitions as physical volumes (if necessary) and then create the volume group with the three volumes. The command will warn you it detects an existing filesystem on any of the devices.

Now we need to create logical volumes on this volume group. You create a logical volume with the next command by giving the name of a new logical volume, its size, and the volume group it will live on:

Now we need to create logical volumes on this volume group. You create a logical volume with the next command by giving the name of a new logical volume, its size, and the volume group it will live on:

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# lvcreate -L <''size''> <''volume_group''> -n <''logical_volume''>

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For example:

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# lvcreate -L 10G VolGroup00 -n lvolhome

# lvcreate -L 10G VolGroup00 -n lvolhome

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This will create a logical volume that you can access later with {{ic|/dev/mapper/Volgroup00-lvolhome}} or {{ic|/dev/VolGroup00/lvolhome}}. Same as with the volume groups, you can use any name you want for your logical volume when creating it.

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To create swap on a logical volume, an additional argument is needed:

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This will create a logical volume that you can access later with {{ic|/dev/VolGroup00/lvolhome}}. Just like volume groups, you can use any name you want for your logical volume when creating it besides a few exceptions listed in {{man|8|lvm|VALID_NAMES}}.

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# lvcreate -C y -L 10G VolGroup00 -n lvolswap

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The {{Ic|-C y}} is used to create a contiguous partition, which means that your swap space does not get partitioned over one or more disks nor over non-contiguous physical extents.

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You can also specify one or more physical volumes to restrict where LVM allocates the data. For example, you may wish to create a logical volume for the root filesystem on your small SSD, and your home volume on a slower mechanical drive. Simply add the physical volume devices to the command line, for example:

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# lvcreate -L 10G VolGroup00 -n lvolhome /dev/sdc1

If you want to fill all the free space left on a volume group, use the next command:

If you want to fill all the free space left on a volume group, use the next command:

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# lvcreate -l +100%FREE VolGroup00 -n lvolmedia

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# lvcreate -l 100%FREE <''volume_group''> -n <''logical_volume''>

You can track created logical volumes with:

You can track created logical volumes with:

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# lvdisplay

# lvdisplay

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{{Note|You may need to load the ''device-mapper'' kernel module ('''modprobe dm-mod''') for the above commands to succeed:}}

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{{Note|You may need to load the ''device-mapper'' kernel module ({{ic|modprobe dm_mod'}}) for the above commands to succeed.}}

{{Tip|You can start out with relatively small logical volumes and expand them later if needed. For simplicity, leave some free space in the volume group so there is room for expansion.}}

{{Tip|You can start out with relatively small logical volumes and expand them later if needed. For simplicity, leave some free space in the volume group so there is room for expansion.}}

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=== Create filesystems and mount logical volumes ===

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=== Create file systems and mount logical volumes ===

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Your logical volumes should now be located in {{ic|/dev/mapper/}} and {{ic|/dev/''YourVolumeGroupName''}}. If you cannot find them, use the next commands to bring up the module for creating device nodes and to make volume groups available:

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Your logical volumes should now be located in {{ic|/dev/''YourVolumeGroupName''/}}. If you cannot find them, use the next commands to bring up the module for creating device nodes and to make volume groups available:

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# modprobe dm-mod

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# modprobe dm_mod

# vgscan

# vgscan

# vgchange -ay

# vgchange -ay

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Now you can create filesystems on logical volumes and mount them as normal partitions (if you are installing Arch linux, refer to [[Beginners' Guide#Mount the partitions|mounting the partitions]] for additional details):

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# mkfs.ext4 /dev/mapper/VolGroup00-lvolhome

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# mount /dev/mapper/VolGroup00-lvolhome /home

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{{Warning|When choosing mountpoints, just select your newly created logical volumes (use: {{ic|/dev/mapper/Volgroup00-lvolhome}}). Do '''not''' select the actual partitions on which logical volumes were created (do not use: {{ic|/dev/sda2}}).}}

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Now you can create file systems on logical volumes and mount them as normal partitions (if you are installing Arch linux, refer to [[mount|mounting the partitions]] for additional details):

{{Warning|When choosing mountpoints, just select your newly created logical volumes (use: {{ic|/dev/Volgroup00/lvolhome}}). Do '''not''' select the actual partitions on which logical volumes were created (do not use: {{ic|/dev/sda2}}).}}

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=== Configure mkinitcpio ===

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In case your root filesystem is on LVM, you will need to enable the appropriate [[mkinitcpio]] hooks, otherwise your system might not boot. Enable:

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* {{ic|udev}} and {{ic|lvm2}} for the default busybox based initramfs

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* {{ic|systemd}} and {{ic|sd-lvm2}} for systemd based initramfs

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=== Add lvm hook to mkinitcpio.conf ===

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{{ic|udev}} is there by default. Edit the file and insert {{ic|lvm2}} between {{ic|block}} and {{ic|filesystems}} like so:

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You'll need to make sure the {{Ic|udev}} and {{Ic|lvm2}} [[mkinitcpio]] hooks are enabled.

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{{hc|1=/etc/mkinitcpio.conf|2=

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HOOKS=(base '''udev''' ... block '''lvm2''' filesystems)

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}}

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{{Ic|udev}} is there by default. Edit the file and insert {{Ic|lvm2}} between {{Ic|block}} and {{Ic|filesystem}} like so:

Afterwards, you can continue in normal installation instructions with the [[Mkinitcpio#Image_creation_and_activation|create an initial ramdisk]] step.

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Afterwards, you can continue in normal installation instructions with the [[mkinitcpio#Image creation and activation|create an initial ramdisk]] step.

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== Configuration ==

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{{Tip|

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* The {{ic|lvm2}} and {{ic|sd-lvm2}} hooks are installed by {{pkg|lvm2}}, not {{pkg|mkinitcpio}}. If you are running ''mkinitcpio'' in an ''arch-chroot'' for a new installation, {{pkg|lvm2}} must be installed inside the ''arch-chroot'' for ''mkinitcpio'' to find the {{ic|lvm2}} or {{ic|sd-lvm2}} hook. If {{pkg|lvm2}} only exists outside the ''arch-chroot'', ''mkinitcpio'' will output {{ic|Error: Hook 'lvm2' cannot be found}}.

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* If your root filesystem is on LVM RAID see [[#Configure mkinitcpio for RAID]].

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}}

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=== Kernel options ===

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If the root file system resides in a logical volume, the {{ic|1=root=}} [[kernel parameter]] must be pointed to the mapped device, e.g {{ic|/dev/''vg-name''/''lv-name''}}.

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== Volume operations ==

=== Advanced options ===

=== Advanced options ===

Line 165:

Line 246:

This is the default by now.

This is the default by now.

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You can restrict the volumes that are activated automatically by setting the {{Ic|auto_activation_volume_list}} in {{Ic|/etc/lvm/lvm.conf}}. If in doubt, leave this option commented out.

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You can restrict the volumes that are activated automatically by setting the {{ic|auto_activation_volume_list}} in {{ic|/etc/lvm/lvm.conf}}. If in doubt, leave this option commented out.

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=== Grow logical volume ===

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=== Resizing volumes ===

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To grow a logical volume you first need to grow the logical volume and then the filesystem to use the newly created free space. Let us say we have a logical volume of 15GB with ext3 on it and we want to grow it to 20G. We need to do the following steps:

If you want to fill all the free space on a volume group, use the next command:

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After extending or prior to reducing the size of a device that has a physical volume on it, you need to grow or shrink the PV using {{ic|pvresize}}.

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# lvextend -l +100%FREE VolGroup00/lvolhome

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{{Warning|Not all filesystems support growing without loss of data and/or growing online.}}

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===== Growing =====

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{{Note|If you do not resize your filesystem, you will still have a volume with the same size as before (volume will be bigger but partly unused).}}

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To expand the PV on {{ic|/dev/sda1}} after enlarging the [[partition]], run:

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=== Shrink logical volume ===

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# pvresize /dev/sda1

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Because your filesystem is probably as big as the logical volume it resides on, you need to shrink the filesystem first and then shrink the logical volume. Depending on your filesystem, you may need to unmount it first. Let us say we have a logical volume of 15GB with ext3 on it and we want to shrink it to 10G. We need to do the following steps:

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This will automatically detect the new size of the device and extend the PV to its maximum.

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# resize2fs /dev/VolGroup00/lvolhome 9G

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# lvreduce -L 10G VolGroup00/lvolhome

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or:

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# lvresize -L -5G VolGroup00/lvolhome

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# resize2fs /dev/VolGroup00/lvolhome

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Here we shrunk the filesystem more than needed so that when we shrunk the logical volume we did not accidentally cut off the end of the filesystem. After that we normally grow the filesystem to fill all free space left on logical volume. You may use {{Ic|lvresize}} instead of {{Ic|lvreduce}}.

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{{Warning|

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{{Note|This command can be done while the volume is online.}}

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* Do not reduce the filesystem size to less than the amount of space occupied by data or you risk data loss.

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* Not all filesystems support shrinking without loss of data and/or shrinking online.

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===== Shrinking =====

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To shrink a physical volume prior to reducing its underlying device, add the {{ic|--setphysicalvolumesize ''size''}} parameters to the command, ''e.g.'':

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# pvresize --setphysicalvolumesize 40G /dev/sda1

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The above command may leave you with this error:

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/dev/sda1: cannot resize to 25599 extents as later ones are allocated.

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0 physical volume(s) resized / 1 physical volume(s) not resized

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Indeed {{ic|pvresize}} will refuse to shrink a PV if it has allocated extents after where its new end would be. One needs to run [[#Move physical extents|pvmove]] beforehand to relocate these elsewhere in the volume group if there is sufficient free space.

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====== Move physical extents ======

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Before moving free extents to the end of the volume, one must run {{ic|pvdisplay -v -m}} to see physical segments. In the below example, there is one physical volume on {{ic|/dev/sdd1}}, one volume group {{ic|vg1}} and one logical volume {{ic|backup}}.

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{{hc|# pvdisplay -v -m|

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Finding all volume groups.

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Using physical volume(s) on command line.

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--- Physical volume ---

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PV Name /dev/sdd1

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VG Name vg1

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PV Size 1.52 TiB / not usable 1.97 MiB

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Allocatable yes

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PE Size 4.00 MiB

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Total PE 399669

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Free PE 153600

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Allocated PE 246069

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PV UUID MR9J0X-zQB4-wi3k-EnaV-5ksf-hN1P-Jkm5mW

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--- Physical Segments ---

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Physical extent 0 to 153600:

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FREE

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Physical extent 153601 to 307199:

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Logical volume /dev/vg1/backup

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Logical extents 1 to 153599

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Physical extent 307200 to 307200:

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FREE

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Physical extent 307201 to 399668:

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Logical volume /dev/vg1/backup

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Logical extents 153601 to 246068

}}

}}

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{{Note|It is better to reduce the filesystem to a smaller size than the logical volume, so that after resizing the logical volume, we do not accidentally cut off some data from the end of the filesystem.}}

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One can observe FREE space are split across the volume. To shrink the physical volume, we must first move all used segments to the beginning.

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Here, the first free segment is from 0 to 153600 and leaves us with 153601 free extents. We can now move this segment number from the last physical extent to the first extent. The command will thus be:

* this command moves 92468 PEs (399668-307200) '''from''' the last segment '''to''' the first segment. This is possible as the first segment encloses 153600 free PEs, which can contain the 92467 moved PEs.

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* the {{ic|--alloc anywhere}} option is used as we move PEs inside the same partition. In case of different partitions, the command would look something like this: {{bc|# pvmove /dev/sdb1:1000-1999 /dev/sdc1:0-999}}

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* this command may take a long time (one to two hours) in case of large volumes. It might be a good idea to run this command in a [[Tmux]] or [[GNU Screen]] session. Any unwanted stop of the process could be fatal.

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* once the operation is complete, run [[fsck]] to make sure your file system is valid.

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}}

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====== Resize physical volume ======

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Once all your free physical segments are on the last physical extent, run {{ic|vgdisplay}} and see your free PE.

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Then you can now run again the command:

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# pvresize --setphysicalvolumesize ''size'' ''PhysicalVolume''

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See the result:

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{{hc|# pvs|

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PV VG Fmt Attr PSize PFree

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/dev/sdd1 vg1 lvm2 a-- 1t 500g

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}}

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====== Resize partition ======

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Last, you need to shrink the partition with your favorite [[Partitioning#Partitioning tools|partitioning tool]].

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==== Logical volumes ====

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{{Note|{{man|8|lvresize}} provides more or less the same options as the specialized {{man|8|lvextend}} and {{man|8|lvreduce}} commands, while allowing to do both types of operation. Notwithstanding this, all those utilities offer a {{ic|-r}}/{{ic|--resizefs}} option which allows to resize the file system together with the LV using {{man|8|fsadm}} (''ext2'', [[ext3]], [[ext4]], ''ReiserFS'' and [[XFS]] supported). Therefore it may be easier to simply use {{ic|lvresize}} for both operations and use {{ic|--resizefs}} to simplify things a bit, except if you have specific needs or want full control over the process.}}

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{{Warning|While enlarging a file system can often be done on-line (''i.e.'' while it is mounted), even for the root partition, shrinking will nearly always require to first unmount the file system so as to prevent data loss. Make sure your FS supports what you are trying to do.}}

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===== Resizing the logical volume and file system in one go =====

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{{Note|Only ''ext2'', [[ext3]], [[ext4]], ''ReiserFS'' and [[XFS]] [[file systems]] are supported. For a different type of file system see [[#Resizing the logical volume and file system separately]].}}

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Extend the logical volume {{ic|mediavol}} in {{ic|MyVolGroup}} by 10 GiB and resize its file system ''all at once'':

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# lvresize -L +10G --resizefs MyVolGroup/mediavol

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Set the size of logical volume {{ic|mediavol}} in {{ic|MyVolGroup}} to 15 GiB and resize its file system ''all at once'':

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# lvresize -L 15G --resizefs MyVolGroup/mediavol

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If you want to fill all the free space on a volume group, use the following command:

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# lvresize -l +100%FREE --resizefs MyVolGroup/mediavol

+

+

See {{man|8|lvresize}} for more detailed options.

+

+

===== Resizing the logical volume and file system separately =====

+

+

For file systems not supported by {{man|8|fsadm}} will need to use the [[File systems#Types of file systems|appropriate utility]] to resize the file system before shrinking the logical volume or after expanding it.

Now expand the file system ([[ext4]] in this example) to the maximum size of the underlying logical volume:

+

+

# resize2fs /dev/MyVolGroup/mediavol

+

+

To reduce the size of logical volume {{ic|mediavol}} in {{ic|MyVolGroup}} by 500 MiB, first calculate the resulting file system size and shrink the file system ([[ext4]] in this example) to the new size:

+

+

# resize2fs /dev/MyVolGroup/mediavol ''NewSize''

+

+

When the file system is shrunk, reduce the size of logical volume:

+

+

# lvresize -L -500M MyVolGroup/mediavol

+

+

See {{man|8|lvresize}} for more detailed options.

+

+

=== Renaming volumes ===

+

+

==== Renaming a Volume Group ====

+

+

Use the {{man|8|vgrename}} command to rename an existing volume group.

+

+

Either of the following commands renames the existing volume group {{ic|vg02}} to {{ic|my_volume_group}}

+

+

# vgrename /dev/vg02 /dev/my_volume_group

+

+

# vgrename vg02 my_volume_group

+

+

==== Renaming Logical Volumes ====

+

+

To rename an existing logical volume, use the {{man|8|lvrename}} command.

+

+

Either of the following commands renames logical volume {{ic|lvold}} in volume group {{ic|vg02}} to {{ic|lvnew}}.

+

+

# lvrename /dev/vg02/lvold /dev/vg02/lvnew

+

+

# lvrename vg02 lvold lvnew

=== Remove logical volume ===

=== Remove logical volume ===

−

{{Warning|Before you remove a logical volume, make sure to move all data that you want to keep somewhere else, otherwise it will be lost!}}

+

{{Warning|Before you remove a logical volume, make sure to move all data that you want to keep somewhere else; otherwise, it will be lost!}}

−

First, find out the name of the logical volume you want to remove. You can get a list of all logical volumes installed on the system with:

+

First, find out the name of the logical volume you want to remove. You can get a list of all logical volumes with:

# lvs

# lvs

−

Next, look up the mountpoint for your chosen logical volume...:

+

Next, look up the mountpoint of the chosen logical volume:

−

$ df -h

+

$ lsblk

−

... and unmount it:

+

Then unmount the filesystem on the logical volume:

−

# umount /your_mountpoint

+

# umount /<''mountpoint''>

Finally, remove the logical volume:

Finally, remove the logical volume:

−

# lvremove /dev/yourVG/yourLV

+

# lvremove <''volume_group''>/<''logical_volume''>

−

Confirm by typing {{ic|y}} and you are done.

+

For example:

−

Do not forget, to update {{ic|/etc/fstab}}!

+

# lvremove VolGroup00/lvolhome

−

You can verify the removal of your logical volume by typing "lvs" as root again (see first step of this section).

+

Confirm by typing in {{ic|y}}.

+

+

Update {{ic|/etc/fstab}} as necessary.

+

+

You can verify the removal of the logical volume by typing {{ic|lvs}} as root again (see first step of this section).

=== Add physical volume to a volume group ===

=== Add physical volume to a volume group ===

Line 228:

Line 448:

You first create a new physical volume on the block device you wish to use, then extend your volume group

You first create a new physical volume on the block device you wish to use, then extend your volume group

−

{{bc|1=

+

# pvcreate /dev/sdb1

−

# pvcreate /dev/sdb1

+

# vgextend VolGroup00 /dev/sdb1

−

# vgextend VolGroup00 /dev/sdb1

−

}}

This of course will increase the total number of physical extents on your volume group, which can be allocated by logical volumes as you see fit.

This of course will increase the total number of physical extents on your volume group, which can be allocated by logical volumes as you see fit.

−

{{Note|It is considered good form to a partition table on your storage medium below LVM, and use the appropriate type code: {{ic|8e}} for MBR, and {{ic|8e00}} for GPT partitions.}}

+

{{Note|It is considered good form to have a [[Partitioning|partition table]] on your storage medium below LVM. Use the appropriate type code: {{ic|8e}} for MBR, and {{ic|8e00}} for GPT partitions.}}

=== Remove partition from a volume group ===

=== Remove partition from a volume group ===

+

+

If you created a logical volume on the partition, [[#Remove logical volume|remove]] it first.

All of the data on that partition needs to be moved to another partition. Fortunately, LVM makes this easy:

All of the data on that partition needs to be moved to another partition. Fortunately, LVM makes this easy:

+

# pvmove /dev/sdb1

# pvmove /dev/sdb1

−

If you want to have the data on a specific physical volume, specify that as the second argument to {{Ic|pvmove}}:

+

+

If you want to have the data on a specific physical volume, specify that as the second argument to {{ic|pvmove}}:

+

# pvmove /dev/sdb1 /dev/sdf1

# pvmove /dev/sdb1 /dev/sdf1

+

Then the physical volume needs to be removed from the volume group:

Then the physical volume needs to be removed from the volume group:

+

# vgreduce myVg /dev/sdb1

# vgreduce myVg /dev/sdb1

+

Or remove all empty physical volumes:

Or remove all empty physical volumes:

+

# vgreduce --all vg0

# vgreduce --all vg0

And lastly, if you want to use the partition for something else, and want to avoid LVM thinking that the partition is a physical volume:

And lastly, if you want to use the partition for something else, and want to avoid LVM thinking that the partition is a physical volume:

+

# pvremove /dev/sdb1

# pvremove /dev/sdb1

+

+

=== Deactivate volume group ===

+

+

Just invoke

+

+

# vgchange -a n my_volume_group

+

+

This will deactivate the volume group and allow you to unmount the container it is stored in.

LVM allows you to take a snapshot of your system in a much more efficient way than a traditional backup. It does this efficiently by using a COW (copy-on-write) policy. The initial snapshot you take simply contains hard-links to the inodes of your actual data. So long as your data remains unchanged, the snapshot merely contains its inode pointers and not the data itself. Whenever you modify a file or directory that the snapshot points to, LVM automatically clones the data, the old copy referenced by the snapshot, and the new copy referenced by your active system. Thus, you can snapshot a system with 35 GiB of data using just 2 GiB of free space so long as you modify less than 2 GiB (on both the original and snapshot). In order to be able to create snapshots you need to have unallocated space in your volume group. Snapshot like any other volume will take up space in the volume group. So, if you plan to use snapshots for backing up your root partition do not allocate 100% of your volume group for root logical volume.

−

−

LVM allows you to take a snapshot of your system in a much more efficient way than a traditional backup. It does this efficiently by using a COW (copy-on-write) policy. The initial snapshot you take simply contains hard-links to the inodes of your actual data. So long as your data remains unchanged, the snapshot merely contains its inode pointers and not the data itself. Whenever you modify a file or directory that the snapshot points to, LVM automatically clones the data, the old copy referenced by the snapshot, and the new copy referenced by your active system. Thus, you can snapshot a system with 35GB of data using just 2GB of free space so long as you modify less than 2GB (on both the original and snapshot).

==== Configuration ====

==== Configuration ====

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You create snapshot logical volumes just like normal ones.

You create snapshot logical volumes just like normal ones.

−

# lvcreate --size 100M --snapshot --name snap01 /dev/mapper/vg0-pv

+

# lvcreate --size 100M --snapshot --name snap01 /dev/vg0/pv

−

With that volume, you may modify less than 100M of data, before the snapshot volume fills up.

+

+

With that volume, you may modify less than 100 MiB of data, before the snapshot volume fills up.

+

+

Reverting the modified 'pv' logical volume to the state when the 'snap01' snapshot was taken can be done with

+

+

# lvconvert --merge /dev/vg0/snap01

+

+

In case the origin logical volume is active, merging will occur on the next reboot (merging can be done even from a LiveCD).

+

+

{{Note|The snapshot will no longer exist after merging.}}

+

+

Also multiple snapshots can be taken and each one can be merged with the origin logical volume at will.

+

+

The snapshot can be mounted and backed up with '''dd''' or '''tar'''. The size of the backup file done with '''dd''' will be the size of the files residing on the snapshot volume.

+

To restore just create a snapshot, mount it, and write or extract the backup to it. And then merge it with the origin.

Snapshots are primarily used to provide a frozen copy of a file system to make backups; a backup taking two hours provides a more consistent image of the file system than directly backing up the partition.

+

+

See [[Create root filesystem snapshots with LVM]] for automating the creation of clean root file system snapshots during system startup for backup and rollback.

+

+

[[dm-crypt/Encrypting an entire system#LVM on LUKS]] and [[dm-crypt/Encrypting an entire system#LUKS on LVM]].

+

+

If you have LVM volumes not activated via the [[initramfs]], [[enable]] {{ic|lvm-monitoring.service}}, which is provided by the {{pkg|lvm2}} package.

+

+

=== LVM cache ===

+

+

From {{man|7|lvmcache}}:

+

+

: The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV. It does this by storing the frequently used blocks on the faster LV. LVM refers to the small fast LV as a cache pool LV. The large slow LV is called the origin LV. Due to requirements from dm-cache (the kernel driver), LVM further splits the cache pool LV into two devices - the cache data LV and cache metadata LV. The cache data LV is where copies of data blocks are kept from the origin LV to increase speed. The cache metadata LV holds the accounting information that specifies where data blocks are stored (e.g. on the origin LV or on the cache data LV). Users should be familiar with these LVs if they wish to create the best and most robust cached logical volumes. All of these associated LVs must be in the same VG.

+

+

==== Create cache ====

+

+

The fast method is creating a PV (if necessary) on the fast disk and add it to the existing volume group:

+

+

# vgextend dataVG /dev/sdx

+

+

Create a cache pool with automatic meta data on sdb, and convert the existing logical volume (dataLV) to a cached volume, all in one step:

−

It is important to have the ''dm-snapshot'' module listed in the MODULES variable of {{ic|/etc/mkinitcpio.conf}}, otherwise the system will not boot. If you do this on an already installed system, make sure to rebuild the image with

Obviously, if you want your cache to be bigger, you can change the {{ic|-L}} parameter to a different size.

−

snapshots are primarily used to provide a frozen copy of a filesystem to make backups; a backup taking two hours provides a more consistent image of the filesystem than directly backing up the partition.

+

{{Note|Cachemode has two possible options:

+

* {{ic|writethrough}} ensures that any data written will be stored both in the cache pool LV and on the origin LV. The loss of a device associated with the cache pool LV in this case would not mean the loss of any data;

+

* {{ic|writeback}} ensures better performance, but at the cost of a higher risk of data loss in case the drive used for cache fails.

−

See [[Create root filesystem snapshots with LVM]] for automating the creation of clean root filesystem snapshots during system startup

+

If a specific {{ic|--cachemode}} is not indicated, the system will assume {{ic|writethrough}} as default.

−

for backup and rollback.

+

}}

−

[[Encrypted_LVM]]

+

==== Remove cache ====

+

+

If you ever need to undo the one step creation operation above:

+

+

# lvconvert --uncache dataVG/dataLV

+

+

This commits any pending writes still in the cache back to the origin LV, then deletes the cache. Other options are available and described in {{man|7|lvmcache}}.

+

+

=== RAID ===

+

+

From {{man|7|lvmraid}}:

+

: {{man|8|lvm}} RAID is a way to create a Logical Volume (LV) that uses multiple physical devices to improve performance or tolerate device failures. In LVM, the physical devices are Physical Volumes (PVs) in a single Volume Group (VG).

will create a 20 GiB mirrored logical volume named "myraid1vol" in VolGroup00 on {{ic|/dev/sda2}} and {{ic|/dev/sdb2}}.

+

+

==== Configure mkinitcpio for RAID ====

+

+

If your root filesystem is on LVM RAID additionally to {{ic|lvm2}} or {{ic|sd-lvm2}} hooks, you need to add {{ic|dm-raid}} and the appropriate RAID modules (e.g. {{ic|raid0}}, {{ic|raid1}}, {{ic|raid10}} and/or {{ic|raid456}}) to the MODULES array in {{ic|mkinitcpio.conf}}.

+

+

For busybox based initramfs:

+

+

{{hc|/etc/mkinitcpio.conf|2=

+

MODULES=('''dm-raid raid0 raid1 raid10 raid456''')

+

HOOKS=(base '''udev''' ... block '''lvm2''' filesystems)

+

}}

+

+

For systemd based initramfs:

+

+

{{hc|/etc/mkinitcpio.conf|2=

+

MODULES=('''dm-raid raid0 raid1 raid10 raid456''')

+

HOOKS=(base '''systemd''' ... block '''sd-lvm2''' filesystems)

+

}}

+

+

== Graphical configuration ==

+

+

There is no "official" GUI tool for managing LVM volumes, but {{AUR|system-config-lvm}} covers most of the common operations, and provides simple visualizations of volume state. It can automatically resize many file systems when resizing logical volumes.

== Troubleshooting ==

== Troubleshooting ==

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Line 619:

* Load proper module:

* Load proper module:

+

# modprobe dm_mod

# modprobe dm_mod

The {{ic|dm_mod}} module should be automatically loaded. In case it does not, you can try:

The {{ic|dm_mod}} module should be automatically loaded. In case it does not, you can try:

+

{{Accuracy|Should module loading at boot be done using "/etc/modules-load.d" instead?}}

−

{{hc|/etc/mkinitcpio.conf:|<nowiki>MODULES="dm_mod ..."</nowiki>}}

+

{{hc|/etc/mkinitcpio.conf|2=

+

MODULES=(dm_mod ...)

+

}}

−

You will need to [[Mkinitcpio#Image_creation_and_activation|rebuild]] the initramfs to commit any changes you made.

+

You will need to [[regenerate the initramfs]] to commit any changes you made.

The reason is that the logical volume was created with an explicit contiguous allocation policy (options {{ic|-C y}} or {{ic|--alloc contiguous}}) and no further adjacent contiguous extents are available (see also [http://www.hostatic.ro/2010/02/15/lvm-inherit-and-contiguous-policies/ reference]).

+

+

To fix this, prior to extending the logical volume, change its allocation policy with {{ic|lvchange --alloc inherit <logical_volume>}}. If you need to keep the contiguous allocation policy, an alternative approach is to move the volume to a disk area with sufficient free extents (see [http://superuser.com/questions/435075/how-to-align-logical-volumes-on-contiguous-physical-extents]).

+

+

=== Command "grub-mkconfig" reports "unknown filesystem" errors ===

+

+

Make sure to remove snapshot volumes before [[GRUB#Generate the main configuration file|generating grub.cfg]].

+

+

=== Thinly-provisioned root volume device times out ===

+

+

With a large number of snapshots, {{ic|thin_check}} runs for a long enough time so that waiting for the root device times out. To compensate, add the {{ic|1=rootdelay=60}} kernel boot parameter to your boot loader configuration.

+

+

=== Delay on shutdown ===

−

In kernel options, you may need {{ic|dolvm}}. {{ic|<nowiki>root=</nowiki>}} should be set to the logical volume, e.g {{ic|/dev/mapper/''vg-name''-''lv-name''}}.

+

If you use RAID, snapshots or thin provisioning and experience a delay on shutdown, make sure {{ic|lvm2-monitor.service}} is [[started]]. See {{Bug|50420}}.

LVM Building Blocks

Logical Volume Management utilizes the kernel's device-mapper feature to provide a system of partitions independent of underlying disk layout. With LVM you abstract your storage and have "virtual partitions", making extending/shrinking easier (subject to potential filesystem limitations).

Virtual partitions allow addition and removal without worry of whether you have enough contiguous space on a particular disk, getting caught up fdisking a disk in use (and wondering whether the kernel is using the old or new partition table), or, having to move other partitions out of the way. This is strictly an ease-of-management solution: LVM adds no security.

Basic building blocks of LVM:

Physical volume (PV)

Partition on hard disk (or even the disk itself or loopback file) on which you can have volume groups. It has a special header and is divided into physical extents. Think of physical volumes as big building blocks used to build your hard drive.

Volume group (VG)

Group of physical volumes used as a storage volume (as one disk). They contain logical volumes. Think of volume groups as hard drives.

Logical volume (LV)

A "virtual/logical partition" that resides in a volume group and is composed of physical extents. Think of logical volumes as normal partitions.

Physical extent (PE)

The smallest size in the physical volume that can be assigned to a logical volume (default 4 MiB). Think of physical extents as parts of disks that can be allocated to any partition.

Advantages

LVM gives you more flexibility than just using normal hard drive partitions:

Use any number of disks as one big disk.

Have logical volumes stretched over several disks.

Create small logical volumes and resize them "dynamically" as they get filled up.

Resize logical volumes regardless of their order on disk. It does not depend on the position of the LV within VG, there is no need to ensure surrounding available space.

Resize/create/delete logical and physical volumes online. File systems on them still need to be resized, but some (such as ext4) support online resizing.

Online/live migration of LV being used by services to different disks without having to restart services.

Snapshots allow you to backup a frozen copy of the file system, while keeping service downtime to a minimum.

Support for various device-mapper targets, including transparent filesystem encryption and caching of frequently used data. This allows creating a system with (one or more) physical disks (encrypted with LUKS) and LVM on top to allow for easy resizing and management of separate volumes (e.g. for /, /home, /backup, etc.) without the hassle of entering a key multiple times on boot.

Disadvantages

Additional steps in setting up the system, more complicated.

If dual-booting, note that Windows does not support LVM; you will be unable to access any LVM partitions from Windows.

Installing Arch Linux on LVM

You should create your LVM Volumes between the partitioning and formatting steps of the installation procedure. Instead of directly formatting a partition to be your root file system, the file system will be created inside a logical volume (LV).

If you use Master Boot Record partition table, set the partition type ID to 8e (partition type Linux LVM in fdisk).

If you use GUID Partition Table, set the partition type GUID to E6D6D379-F507-44C2-A23C-238F2A3DF928 (partition type Linux LVM in fdisk and 8e00 in gdisk).

Create your physical volumes (PVs). If you have one disk it is best to just create one PV in one large partition. If you have multiple disks you can create partitions on each of them and create a PV on each partition.

Create physical volumes

Warning: Make sure you target the correct device, or below commands will result in data loss!

Create a physical volume on them:

# pvcreate DEVICE

This command creates a header on each device so it can be used for LVM. As defined in #LVM Building Blocks, DEVICE can be a disk (e.g. /dev/sda), a partition (e.g. /dev/sda2) or a loop back device. For example:

Note: You can create more than one volume group if you need to, but then you will not have all your storage presented as one disk.

Create in one step

LVM allows you to combine the creation of a volume group and the physical volumes in one easy step. For example, to create the group VolGroup00 with the three devices mentioned above, you can run:

# vgcreate VolGroup00 /dev/sda2 /dev/sdb1 /dev/sdc

This command will first set up the three partitions as physical volumes (if necessary) and then create the volume group with the three volumes. The command will warn you it detects an existing filesystem on any of the devices.

Create logical volumes

Tip: If you wish to use snapshots, logical volume caching, thin provisioned logical volumes or RAID see #Logical volume types.

Now we need to create logical volumes on this volume group. You create a logical volume with the next command by giving the name of a new logical volume, its size, and the volume group it will live on:

# lvcreate -L <size> <volume_group> -n <logical_volume>

For example:

# lvcreate -L 10G VolGroup00 -n lvolhome

This will create a logical volume that you can access later with /dev/VolGroup00/lvolhome. Just like volume groups, you can use any name you want for your logical volume when creating it besides a few exceptions listed in lvm(8).

You can also specify one or more physical volumes to restrict where LVM allocates the data. For example, you may wish to create a logical volume for the root filesystem on your small SSD, and your home volume on a slower mechanical drive. Simply add the physical volume devices to the command line, for example:

# lvcreate -L 10G VolGroup00 -n lvolhome /dev/sdc1

If you want to fill all the free space left on a volume group, use the next command:

# lvcreate -l 100%FREE <volume_group> -n <logical_volume>

You can track created logical volumes with:

# lvdisplay

Note: You may need to load the device-mapper kernel module (modprobe dm_mod') for the above commands to succeed.

Tip: You can start out with relatively small logical volumes and expand them later if needed. For simplicity, leave some free space in the volume group so there is room for expansion.

Create file systems and mount logical volumes

Your logical volumes should now be located in /dev/YourVolumeGroupName/. If you cannot find them, use the next commands to bring up the module for creating device nodes and to make volume groups available:

# modprobe dm_mod
# vgscan
# vgchange -ay

Now you can create file systems on logical volumes and mount them as normal partitions (if you are installing Arch linux, refer to mounting the partitions for additional details):

Warning: When choosing mountpoints, just select your newly created logical volumes (use: /dev/Volgroup00/lvolhome). Do not select the actual partitions on which logical volumes were created (do not use: /dev/sda2).

Configure mkinitcpio

In case your root filesystem is on LVM, you will need to enable the appropriate mkinitcpio hooks, otherwise your system might not boot. Enable:

udev and lvm2 for the default busybox based initramfs

systemd and sd-lvm2 for systemd based initramfs

udev is there by default. Edit the file and insert lvm2 between block and filesystems like so:

The lvm2 and sd-lvm2 hooks are installed by lvm2, not mkinitcpio. If you are running mkinitcpio in an arch-chroot for a new installation, lvm2 must be installed inside the arch-chroot for mkinitcpio to find the lvm2 or sd-lvm2 hook. If lvm2 only exists outside the arch-chroot, mkinitcpio will output Error: Hook 'lvm2' cannot be found.

Indeed pvresize will refuse to shrink a PV if it has allocated extents after where its new end would be. One needs to run pvmove beforehand to relocate these elsewhere in the volume group if there is sufficient free space.

Move physical extents

Before moving free extents to the end of the volume, one must run pvdisplay -v -m to see physical segments. In the below example, there is one physical volume on /dev/sdd1, one volume group vg1 and one logical volume backup.

One can observe FREE space are split across the volume. To shrink the physical volume, we must first move all used segments to the beginning.

Here, the first free segment is from 0 to 153600 and leaves us with 153601 free extents. We can now move this segment number from the last physical extent to the first extent. The command will thus be:

this command moves 92468 PEs (399668-307200) from the last segment to the first segment. This is possible as the first segment encloses 153600 free PEs, which can contain the 92467 moved PEs.

the --alloc anywhere option is used as we move PEs inside the same partition. In case of different partitions, the command would look something like this:

# pvmove /dev/sdb1:1000-1999 /dev/sdc1:0-999

this command may take a long time (one to two hours) in case of large volumes. It might be a good idea to run this command in a Tmux or GNU Screen session. Any unwanted stop of the process could be fatal.

once the operation is complete, run fsck to make sure your file system is valid.

Resize physical volume

Once all your free physical segments are on the last physical extent, run vgdisplay and see your free PE.

Then you can now run again the command:

# pvresize --setphysicalvolumesize sizePhysicalVolume

See the result:

# pvs

PV VG Fmt Attr PSize PFree
/dev/sdd1 vg1 lvm2 a-- 1t 500g

Resize partition

Logical volumes

Note:lvresize(8) provides more or less the same options as the specialized lvextend(8) and lvreduce(8) commands, while allowing to do both types of operation. Notwithstanding this, all those utilities offer a -r/--resizefs option which allows to resize the file system together with the LV using fsadm(8) (ext2, ext3, ext4, ReiserFS and XFS supported). Therefore it may be easier to simply use lvresize for both operations and use --resizefs to simplify things a bit, except if you have specific needs or want full control over the process.

Warning: While enlarging a file system can often be done on-line (i.e. while it is mounted), even for the root partition, shrinking will nearly always require to first unmount the file system so as to prevent data loss. Make sure your FS supports what you are trying to do.

Snapshots

LVM allows you to take a snapshot of your system in a much more efficient way than a traditional backup. It does this efficiently by using a COW (copy-on-write) policy. The initial snapshot you take simply contains hard-links to the inodes of your actual data. So long as your data remains unchanged, the snapshot merely contains its inode pointers and not the data itself. Whenever you modify a file or directory that the snapshot points to, LVM automatically clones the data, the old copy referenced by the snapshot, and the new copy referenced by your active system. Thus, you can snapshot a system with 35 GiB of data using just 2 GiB of free space so long as you modify less than 2 GiB (on both the original and snapshot). In order to be able to create snapshots you need to have unallocated space in your volume group. Snapshot like any other volume will take up space in the volume group. So, if you plan to use snapshots for backing up your root partition do not allocate 100% of your volume group for root logical volume.

Configuration

You create snapshot logical volumes just like normal ones.

# lvcreate --size 100M --snapshot --name snap01 /dev/vg0/pv

With that volume, you may modify less than 100 MiB of data, before the snapshot volume fills up.

Reverting the modified 'pv' logical volume to the state when the 'snap01' snapshot was taken can be done with

# lvconvert --merge /dev/vg0/snap01

In case the origin logical volume is active, merging will occur on the next reboot (merging can be done even from a LiveCD).

Note: The snapshot will no longer exist after merging.

Also multiple snapshots can be taken and each one can be merged with the origin logical volume at will.

The snapshot can be mounted and backed up with dd or tar. The size of the backup file done with dd will be the size of the files residing on the snapshot volume.
To restore just create a snapshot, mount it, and write or extract the backup to it. And then merge it with the origin.

Snapshots are primarily used to provide a frozen copy of a file system to make backups; a backup taking two hours provides a more consistent image of the file system than directly backing up the partition.

LVM cache

The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV. It does this by storing the frequently used blocks on the faster LV. LVM refers to the small fast LV as a cache pool LV. The large slow LV is called the origin LV. Due to requirements from dm-cache (the kernel driver), LVM further splits the cache pool LV into two devices - the cache data LV and cache metadata LV. The cache data LV is where copies of data blocks are kept from the origin LV to increase speed. The cache metadata LV holds the accounting information that specifies where data blocks are stored (e.g. on the origin LV or on the cache data LV). Users should be familiar with these LVs if they wish to create the best and most robust cached logical volumes. All of these associated LVs must be in the same VG.

Create cache

The fast method is creating a PV (if necessary) on the fast disk and add it to the existing volume group:

# vgextend dataVG /dev/sdx

Create a cache pool with automatic meta data on sdb, and convert the existing logical volume (dataLV) to a cached volume, all in one step:

Obviously, if you want your cache to be bigger, you can change the -L parameter to a different size.

Note: Cachemode has two possible options:

writethrough ensures that any data written will be stored both in the cache pool LV and on the origin LV. The loss of a device associated with the cache pool LV in this case would not mean the loss of any data;

writeback ensures better performance, but at the cost of a higher risk of data loss in case the drive used for cache fails.

If a specific --cachemode is not indicated, the system will assume writethrough as default.

Remove cache

If you ever need to undo the one step creation operation above:

# lvconvert --uncache dataVG/dataLV

This commits any pending writes still in the cache back to the origin LV, then deletes the cache. Other options are available and described in lvmcache(7).

RAID

lvm(8) RAID is a way to create a Logical Volume (LV) that uses multiple physical devices to improve performance or tolerate device failures. In LVM, the physical devices are Physical Volumes (PVs) in a single Volume Group (VG).

will create a 20 GiB mirrored logical volume named "myraid1vol" in VolGroup00 on /dev/sda2 and /dev/sdb2.

Configure mkinitcpio for RAID

If your root filesystem is on LVM RAID additionally to lvm2 or sd-lvm2 hooks, you need to add dm-raid and the appropriate RAID modules (e.g. raid0, raid1, raid10 and/or raid456) to the MODULES array in mkinitcpio.conf.

Graphical configuration

There is no "official" GUI tool for managing LVM volumes, but system-config-lvmAUR covers most of the common operations, and provides simple visualizations of volume state. It can automatically resize many file systems when resizing logical volumes.

Troubleshooting

Changes that could be required due to changes in the Arch-Linux defaults

The use_lvmetad = 1 must be set in /etc/lvm/lvm.conf. This is the default now - if you have a lvm.conf.pacnew file, you must merge this change.

LVM commands do not work

Load proper module:

# modprobe dm_mod

The dm_mod module should be automatically loaded. In case it does not, you can try:

The factual accuracy of this article or section is disputed.

Reason: Should module loading at boot be done using "/etc/modules-load.d" instead? (Discuss in Talk:LVM#)

Logical Volumes do not show up

If you are trying to mount existing logical volumes, but they do not show up in lvscan, you can use the following commands to activate them:

# vgscan
# vgchange -ay

LVM on removable media

Symptoms:

# vgscan

Reading all physical volumes. This may take a while...
/dev/backupdrive1/backup: read failed after 0 of 4096 at 319836585984: Input/output error
/dev/backupdrive1/backup: read failed after 0 of 4096 at 319836643328: Input/output error
/dev/backupdrive1/backup: read failed after 0 of 4096 at 0: Input/output error
/dev/backupdrive1/backup: read failed after 0 of 4096 at 4096: Input/output error
Found volume group "backupdrive1" using metadata type lvm2
Found volume group "networkdrive" using metadata type lvm2

Cause:

Removing an external LVM drive without deactivating the volume group(s) first. Before you disconnect, make sure to:

# vgchange -an volume group name

Fix: assuming you already tried to activate the volume group with vgchange -ay vg, and are receiving the Input/output errors:

# vgchange -an volume group name

Unplug the external drive and wait a few minutes:

# vgscan
# vgchange -ay volume group name

Resizing a contiguous logical volume fails

The reason is that the logical volume was created with an explicit contiguous allocation policy (options -C y or --alloc contiguous) and no further adjacent contiguous extents are available (see also reference).

To fix this, prior to extending the logical volume, change its allocation policy with lvchange --alloc inherit <logical_volume>. If you need to keep the contiguous allocation policy, an alternative approach is to move the volume to a disk area with sufficient free extents (see [1]).

Command "grub-mkconfig" reports "unknown filesystem" errors

Thinly-provisioned root volume device times out

With a large number of snapshots, thin_check runs for a long enough time so that waiting for the root device times out. To compensate, add the rootdelay=60 kernel boot parameter to your boot loader configuration.

Delay on shutdown

If you use RAID, snapshots or thin provisioning and experience a delay on shutdown, make sure lvm2-monitor.service is started. See FS#50420.